Question: $ { \left[\begin{array}{rr}{-1} & {3} \\ {0} & {3} \\ {0} & {4}\end{array}\right]+\left[\begin{array}{rr}{-2} & {4} \\ {1} & {1} \\ {2} & {-1}\end{array}\right] = {?} } $
To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{rr}{-1}+{-2} & {3}+{4} \\ {0}+{1} & {3}+{1} \\ {0}+{2} & {4}+{-1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{rr}{-3} & {7} \\ {1} & {4} \\ {2} & {3}\end{array}\right]}$